Performance evaluation of smoothing algorithms for transmittingprerecorded variable-bit-rate video

The transfer of prerecorded, compressed variable-bit-rate video requires multimedia services to support large fluctuations in bandwidth requirements on multiple time scales. Bandwidth smoothing techniques can reduce the burstiness of a variable-bit-rate stream by transmitting data at a series of fixed rates, simplifying the allocation of resources in video servers and the communication network. This paper compares the transmission schedules generated by the various smoothing algorithms, based on a collection of metrics that relate directly to the server, network, and client resources necessary for the transmission, transport, and playback of prerecorded video. Using MPEG-1 and MJPEG video data and a range of client buffer sizes, we investigate the interplay between the performance metrics and the smoothing algorithms. The results highlight the unique strengths and weaknesses of each bandwidth smoothing algorithm, as well as the characteristics of a diverse set of video clips     

BGP routing policies in ISP networks

The Internet has quickly evolved into a vast global network owned and operated by thousands of different administrative entities. During this time, it became apparent that vanilla shortest path routing would be insufficient to handle the myriad operational, economic, and political factors involved in routing. ISPs began to modify routing configurations to support routing policies - goals held by the router's owner that controlled which routes were chosen and which routes were propagated to neighbors. BGP, originally a simple path vector protocol, was incrementally modified over time with a number of mechanisms to support policies, adding substantially to the complexity. Much of the mystery in BGP comes not only from the protocol complexity, but also from a lack of understanding of the underlying policies and the problems ISPs face that are addressed by these policies. In this article we shed light on goals operators have and their resulting routing policies, why BGP evolved the way it did, and how common policies are implemented using BGP. We also discuss recent and current work in the field that aims to address problems that arise in applying and supporting routing policies.     

Efficient policies for carrying Web traffic over flow-switchednetworks

To efficiently transfer diverse traffic over high-speed links, modern integrated networks require more efficient packet-switching techniques that can capitalize on the advances in switch hardware. Several promising approaches attempt to improve the performance by creating dedicated “shortcut” connections for long-lived traffic flows, at the expense of the network overhead for establishing and maintaining these shortcuts. The network can balance these cost-performance tradeoffs through three tunable parameters: the granularity of flow end-point addresses, the timeout for grouping related packets into flows, and the trigger for migrating a long-lived flow to a shortcut connection. Drawing on a continuous one-week trace of Internet traffic, we evaluate the processor and switch overheads for transferring HTTP server traffic through a flow-switched network. In contrast to previous work, we focus on the full probability distributions of flow sizes and cost-performance metrics to highlight the subtle influence of the HTTP protocol and user behavior on the performance of flow switching. We find that moderate levels of aggregation and triggering yield significant reductions in overhead with a negligible reduction in performance. The traffic characterization results further suggest schemes for limiting shortcut overhead by temporarily delaying the creation of shortcuts during peak load and by aggregating related packets that share a portion of their routes through the network     

Design for configurability: rethinking interdomain routing policies from the ground up

Giving ISPs more fine-grain control over interdomain routing policies would help them better manage their networks and offer value-added services to their customers. Unfortunately, the current BGP route-selection process imposes inherent restrictions on the policies an ISP can configure, making many useful policies infeasible. In this paper, we present Morpheus, a routing control platform that is designed for configurability. Morpheus enables a single ISP to safely realize a much broader range of routing policies without requiring changes to the underlying routers or the BGP protocol itself. Morpheus allows network operators to: (1) make flexible trade-offs between policy objectives through a weighted-sum based decision process, (2) realize customer-specific policies by supporting multiple route-selection processes in parallel, and allowing customers to influence the decision processes, and (3) configure the decision processes through a simple and intuitive configuration interface based on the Analytic Hierarchy Process, a decision-theoretic technique for balancing conflicting objectives. We also present the design, implementation, and evaluation of Morpheus as an extension to the XORP software router.     

Network-Wide Prediction of BGP Routes

This paper presents provably correct algorithms for computing the outcome of the BGP route-selection process for each router in a network, without simulating the complex details of BGP message passing. The algorithms require only static inputs that can be easily obtained from the routers: the BGP routes learned from neighboring domains, the import policies configured on the BGP sessions, and the internal topology. Solving the problem would be easy if the route-selection process were deterministic and every router received all candidate BGP routes. However, two important features of BGP-the Multiple Exit Discriminator (MED) attribute and route reflectors-violate these properties. After presenting a simple route-prediction algorithm for networks that do not use these features, we present algorithms that capture the effects of the MED attribute and route reflectors in isolation. Then, we explain why the interaction between these two features precludes efficient route prediction. These two features also create difficulties for the operation of BGP itself, leading us to suggest improvements to BGP that achieve the same goals as MED and route reflection without introducing the negative side effects     

With the society

The following is a digest of a statement on pending fire prevention and control legislation that was made by Gerald L. Maatman, SFPE, President of the National Loss Control Service Corporation (a subsidiary of Kemperco) to the Subcommittee on Science, Research, and Development; Committee on Science and Astronautics; United States House of Representatives on August 1, 1973. The statement, which was released by Kemperco, is an expression of Mr. Maatman’s views, which also represent those of the Kemper Insurance Group.     

A STUDY OF AN ALUMINA-SILICA CHECKER BRICK FROM THE REGENERATOR OF A GLASS TANK *

At the end of a campaign, alumina-silica checker brick in glass-tank regenerators occasionally are found to have undergone partial destruction as a result of the separation of an altered surface layer of the brick from the less affected core. In an investigation of such an occurrence, it was found that the outer layer had largely been converted to nephelite by reaction of soda vapors and dust from the glass batch with mullite and corundum in the brick. Thermal expansion determinations showed that the rate of reversible thermal expansion in the altered layer was almost twice as great as that of the unaltered brick. It is concluded that the separation or slabbing of the altered layer was due in part to this difference in thermal expansion and in part to a permanent expansion of the slabbed layer which occurred apparently when portions of the brick substance were converted to nephelite.     

Evaluating the impact of stale link state on quality-of-servicerouting

Quality-of-service (QoS) routing satisfies application performance requirements and optimizes network resource usage by selecting paths based on connection traffic parameters and link load information. However, distributing link state imposes significant bandwidth and processing overhead on the network. This paper investigates the performance tradeoff between protocol overhead and the quality of the routing decisions in the context of the source-directed link state routing protocols proposed for IP and ATM networks. We construct a detailed model of QoS routing that parameterizes the path-selection algorithm, link-cost function, and link state update policy. Through extensive simulation experiments with several network topologies and traffic patterns, we uncover the effects of stale link state information and random fluctuations in traffic load on the routing and setup overheads. We then investigate how inaccuracy of link state information interacts with the size and connectivity of the underlying topology. Finally, we show that tuning the coarseness of the link-cost metric to the inaccuracy of underlying link state information reduces the computational complexity of the path-selection algorithm without significantly degrading performance. This work confirms and extends earlier studies, and offers new insights for designing efficient quality-of-service routing policies in large networks